1. Field of the Invention
This invention relates to the field of automatic transmission torque converters, which hydrodynamically connect an impeller wheel to a turbine wheel The invention pertains particularly to a bypass clutch, which mechanically connects the turbine and impeller, bypassing the hydrokinetic connection between them, and releases the turbine and impeller, thereby reestablishing the hydrokinetic effect.
2. Description of the Prior Art
The transaxle described in U.S. Pat. No. 4,509,389, which is assigned to the assignee of my invention, includes a hydrokinetic torque converter having an impeller and a turbine. The housing for the impeller includes a lockup clutch assembly having a clutch plate that engages a friction surface on the impeller housing. The clutch plate carries friction material that establishes a frictional driving connection between the impeller and the turbine when the pressure differential across the clutch plate is sufficient to establish a clutch-engaging force.
The clutch plate is connected through a damper assembly to the hub of the turbine, thus establishing a mechanical torque transfer between an engine crankshaft and the turbine shaft, which bypasses the hydrokinetic torque flow path through the torque converter.
Converter lockup clutch constructions are well known in the art, an early prior art teaching being described in U.S. Pat. No. 3,252,352, which is assigned to the assignee of this invention. Another example of early prior art torque converter assemblies having a lockup clutch is disclosed in U.S. Pat. No. 3,541,893.
More recent prior art teachings include means for controlling the application of the torque converter clutch by means of an electronic controller that establishes a modification of the clutch engaging force under certain operating conditions, for example, during shifts when it is desired to eliminate undesired torque fluctuations and engine speed changes during transient periods when torque flow interruption is desired. The electronic controller establishes a pressure force on the clutch plate that is adequate to meet the transient torque transmission requirements of the driveline. Examples of this are shown in U.S. Pat. Nos. 4,560,043 and 4,301,900.
U.S. Pat. No. 3,541,893, which also is assigned to the assignee of this invention, includes a clutch capacity modulator valve that establishes a desired pressure in the clutch pressure control chamber defined by the impeller housing and the clutch plate. The controls for establishing the clutch capacity is intended to eliminate excess torque capacity so that the clutch will be maintained in the engaged condition under driving conditions when clutch engagement is desired, but excess clutch capacity is avoided by controlling the pressure differential across the clutch plate. This contributes to more precise lockup clutch control and eliminates undesired torque fluctuations upon clutch application and release.
It is also known in the prior art to effect a continuous slipping of a lockup clutch or bypass clutch for a hydrokinetic torque converter by continuously modulating the pressure that controls the clutch. An example of a continuously slipping bypass clutch, actuated by the pressure in the torus circuit of the converter, is disclosed in U.S. Pat. No. 4,468,988. Another example is disclosed in U.S. Pat. No. 4,662,488.
U.S. Pat. No. 4,926,988 describes a hydrodynamic clutch having a first disc, located between a piston and a second disc, carried on an impeller wheel. The piston is rotatably supported on, and driveably connected to the impeller.
U.S. Pat. No. 5,056,631 describes a torque converter clutch having a hydraulically actuated piston that carries friction material and a clutch disc. Flow passages are formed in the friction material to permit fluid flow to carry heat from the friction surface and clutch plate.